1. Field of the Invention
This invention generally relates to a method and apparatus for testing the wheels of a vehicle and in particular to a method and apparatus for measuring the inclination of the wheels of a vehicle, such as an automobile. More specifically, the present invention relates to a method and apparatus for measuring the toe-in/toe out of each of the wheels of a vehicle.
2. Description of the Prior Art
An automobile generally has four wheels which are arranged in particular orientations from various considerations. For example, the front wheels are arranged in consideration of such parameters as toe-in/toe-out, camber, caster and kingpin angle so as to secure stability in steering operation. It is often required to determine these parameters properly in order to secure the running stability of an automobile as a whole. Above all, proper setting of toe-in/toe-out condition is extremely important because this setting is directly related to the operative association between the steering wheel and the direction of movement of the automobile.
Although it is well known for one skilled in the art, the toe-in/toe-out condition will be explained with reference to FIG. 1 for the sake of clarity. The particular arrangement of wheels 2, 2 of an automobile 1 illustrated in FIG. 2 indicates the toe-in condition, wherein, when viewed from above in plan view, the wheels 2, 2 are inclined inwardly with respect to the forward direction D of movement of the automobile 1. Toe-out is the condition in which the wheels 2, 2 are inclined outwardly, i.e., the rear parts of the wheels 2, 2 are closer together than the forward parts of the wheels 2, 2 with respect to the forward direction D of movement of the automobile 1. For the matter of convenience, here, the angle .theta. defined between the forward direction D of movement of the automobile 1 and the center plane of each of the wheels 2, as shown in FIG. 1, will be referred to as a toe angle.
In order to set the steering wheel of an automobile properly with respect to the direction of advancement of the automobile or the imaginary center line extending from the front to the rear, it is required to first measure the inclination of each of the right and left wheels with respect to the center plane of the automobile, i.e., the toe angle of each of the right and left wheels, and to adjust the inclination of each of the left and right wheels until they become symmetrically inclined with respect to the center plane of the automobile. Any of the prior art methods and apparatus for measuring the toe angle was appreciably affected by various measuring conditions, including the size and kind of tires encircling and fitting the rim of the wheels and the air pressure of each of these tires, and, thus, it was extremely difficult to measure the toe angle at high accuracy. Among the prior art systems for measuring the toe angle of a wheel, there was one using a detector plate which was pressed against the outer side surface of a wheel for measuring the toe angle thereof. In this case, however, there were variations in the suspension system as a whole when the detector plate was pressed against the wheel, so that accurate measurement could not be carried out.
Recently, automobiles having four wheels which are all independently suspended have become increasingly popular because of riding comfort and reduction of weight. In such automobiles having independently suspended front and rear wheels, it is necessary to check and adjust each of the four wheels from time to time.